Compounds capable of absorbing and/or emitting light can be ideally suited for use in a wide variety of optical and electroluminescent devices, including, for example, photo-absorbing devices such as solar- and photo-sensitive devices, OLEDs, and photo-emitting devices. Much research has been devoted to the discovery and optimization of organic and organometallic materials for using in optical and electroluminescent devices. Generally, research in this area aims to accomplish a number of goals, including improvements in absorption and emission efficiency and improvements in the stability of devices, as well as improvements in processing ability.
Despite significant advances in research devoted to optical and electro-optical materials (e.g., red and green phosphorescent organometallic materials are commercially available and have been used as phosphors in OLEDs, lighting and advanced displays), many currently available materials exhibit a number of disadvantages, including poor processing ability, inefficient emission or absorption, and less than ideal stability, among others.
Good blue emitters are particularly scarce, with one challenge being the stability of the blue devices. The choice of the host materials has an impact on the stability and the efficiency of the devices. The lowest triplet excited state energy of the blue phosphors is very high compared with that of the red and green phosphors, which means that the lowest triplet excited state energy of host materials for the blue devices should be even higher. Thus, one of the problems is that there are limited host materials to be used for the blue devices.
Cyclometalated metal complexes have found wide applications as emitters for OLEDs in recent decades. Much attention has been paid to the development of new improved materials for both display and solid state lighting applications. So far, most of the reported platinum (II) and palladium (II) emitters are acyclic, cyclic platinum (II) and palladium (II) emitters have been rarely reported even if cyclic ones are potentially more stable compared with acyclic ones. A need exists for new materials an improved the color purity, enhanced operational stability as well as elimination of the potential intermolecular interaction. The present application addresses these needs.